The present invention relates generally to article-supporting fasteners and, more particularly, to expansion fasteners as are used with drywall or similar plaster boards in building construction.
Numerous different expansion fasteners are known. These devices are often used to retain pictures, ornaments or other articles directly to the interior building wall. These walls are typically nailed or glued to skeletal frame members of the building and subsequently covered with paint or wallpaper. Once so covered, it is usually difficult to locate the underlying frame members. Thus, drywall fasteners tend to rely only upon the support strength of the drywall board itself.
Two general types of drywall expansion fasteners are known: those that require prior drilling or punching through the wall to permit fastener insertion, and those that are self-penetrating in that they may be directly hammered, punched or screwed into the wall. The latter type of fasteners are typically referred to as "drive-in fasteners" and tend to be preferred since they permit quicker installation. However, prior drive-in fasteners frequently cannot support the same loads as fasteners using preformed holes since the act of penetrating the wall within drive-in fasteners tends to create a blow out on the back side of the wall.
Blow outs are believed to result from the fact that prior drive-in fasteners pushed the wall material aside and forward during penetration. This displaced material appears to weaken the adjacent wall structure and create a larger opening at the side of the wall opposite the initial penetration of the fastener. A typical blow out situation is shown in FIG. 1. Fastener 10 (shown only in part) penetrated wall 12 from left to right. The initial penetration opening has a width of I. The opening created by the blow out has a significantly larger width B. As a result, load support within the walls for the fastener is available only for a distance L where the width of the hole closely corresponds to the width of fastener 10. As a general rule, the larger L becomes, the more load the fastener can support.
Blow outs can also be a problem for fasteners using pre-formed holes, but, for example, careful drilling can minimize the occurrence of blow outs. Unfortunately, such drilling is time-consuming and, especially where a large number of fasteners are needed, can result in significantly higher construction costs.
Construction costs are also affected by the price of the fastener itself. To retain the fastener in the wall, a portion of the fastener which has penetrated the wall often expands so as to prevent the fastener from being withdrawn from the hole created in the wall. This expansion can occur within the hole or past the hole on the back side of the wall. The mechanisms which create this expansion are sometimes elaborate and can significantly increase fastener production costs.
Typically, it is also important not to create bulges in the wall surrounding the fastener when expanding the fastener to retain it in the wall. These bulges can be unsightly and can structurally weaken the wall. Thus, stress control in fastener expansion can be critical. At the same time, since such controlled expansion is often accomplished by threaded rotation of elements within the fastener, the fastener should be fixed so as to avoid relative rotation with respect to the wall when these elements are adjusted.
Mechanisms for controlled fastener expansion are often expensive and require specially formed parts. Some prior fasteners have been constructed to reduce those costs by permitting expansion adjustment, through ordinary screws provided by the installer. Unfortunately, the torque required to insert those screws is frequently so high that installation of a number of those fasteners becomes overly tiring and/or time consuming. In addition, it is common that a particular fastener of that type will only accept one size screw. On the other hand, fasteners which are adjustable by extremely low threading torque sometimes give no indication of when the fastener has bottomed out and is fully engaged with the back of the wall. As a result, the installer may not realize when to stop threading and may cause serious damage to the wall, if threading too far, or inadequately secure the fastener, if not threading far enough.
It is, therefore, an object of the present invention to provide an improved expansion fastener which overcomes limitations in prior fasteners.
Another object is the provision of a drive-in fastener which avoids creation of blow outs in drywall and plaster boards.
A further object is to provide an inexpensive drive-in fastener which is readily secured within the wall.
Still another object is the provision of a reliable expansion fastener having expansion stress control during installation.
Yet another object is to provide an expansion fastener with increased load capacity in both wall and ceiling applications.
Still a further object is the provision of a drive-in expansion fastener which is easily threaded into place by ordinary screws of various sizes.
These and other objects of the present invention are attained by, the provision of a drive-in expansion fastener having a generally cylindrical, hollow body with a tapered end formed from an angular truncation of the body. The body is reinforced by at least one longitudinal rib so as to permit drive-in penetration from the tapered end even if the fastener is formed from plastic materials. The fastener is retained within the wall by at least one pair of hinged flanges which .[.expand.]. .Iadd.move apart .Iaddend.circumferentially .Iadd.when the fastener is expanded radially .Iaddend.in response to threaded insertion of an ordinary screw within the hollow portion of the body. That screw engages an inclined surface within the body to cam the flanges .Iadd.radially .Iaddend.outwardly .Iadd.and circumferentially apart.Iaddend.. The flanges engage the back surface of the wall while a longitudinally slit portion of the body expands within the hole created by drive-in penetration.
The present invention avoids blow outs by creating a clean cut through the board with the tapered end and receiving cut out debris within the fastener as the penetration is made. Thus, destructive stress within the wall beyond the penetration hole is minimized. The fastener can be molded from a self-lubricating nylon so as to minimize the necessary adjustment torque. Installation is completed when the screw is bottomed out against a thin, base shoulder on the front surface of the wall. Threading the adjustment screw primarily causes the hinged flanges to move .Iadd.radially .Iaddend.outwardly .Iadd.and circumferentially apart .Iaddend.along the back surface of the wall, rather than into it. Thus, bottoming out the screw on the base shoulder avoids creating bulges and undesired expansion stress within the wall.
Other objects, advantages and novel features of the present invention will now become readily apparent upon consideration of the following description of preferred embodiments in conjunction with the drawings.